There are various known assist arms which can be fitted to exoskeletons, and can be used in particular for lifting loads from below, for example a sack of sand or a patient. In general, these arms have shoulder, elbow and wrist articulations that are associated with respective motorizations, which makes the assembly heavy and complex. Furthermore, the motorizations are often in the form of transverse motors extending in continuation of the axis of the articulation, which entails significant encumbrance. In order to limit this encumbrance, it is therefore expedient to restrict the load which can be lifted, or to increase the down-gearing ratio between the motor and the driven segment, which tends to reduce the transparency of the articulation. This drawback may be partially overcome by torque feedback, but this requires the use of a torque sensor, making the solution less reliable, more complex and more expensive.
There are other solutions, for example lifting components which can be fitted to an exoskeleton and which comprise spring balancing instead of an actuator. Such a component needs to be adjusted beforehand for a given load, which greatly limits the range of its use.